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Food supermarket refrigerated showcase principle of preservation (four)

author: supermarket refrigerated showcase category: walk-in display coolers Views: 578Time: 2016-08-22

food supermarket refrigerated showcase principle of preservation (four)

Food changes color in the supermarket refrigerated showcase, and the food will be frozen and frozen. Except for food discoloration caused by refrigerant leakage (such as ammonia leakage

, the red of carrots will turn blue: the white of onions, cabbage, and lotus seeds will turn yellow), and other discoloration that occurs at room temperature , It will happen during the long-term freezing process of

, but the speed of change appears very slow. The discoloration that occurs during freezing is mainly the discoloration of frozen aquatic products. From the appearance of

, there are usually browning, blackening, and fading. The reasons for the discoloration of aquatic products include the decomposition of natural color and the production of new discoloration substances. The natural color is broken

, such as the fading of red fish skin, the discoloration of frozen tuna, etc., and new discoloration substances such as blackening of shrimps and browning of crocodile meat are produced. Discoloration not only worsens the appearance of aquatic products

, but sometimes also produces peculiar smell, which affects the quality of frozen products.

protein freeze denaturation. In animal foods such as fish and meat, the main protein that constitutes muscle is myofibril protein. During the freezing process, myofibril protein

white matter will undergo freezing denaturation, which is manifested as a decrease in salt solubility, a decrease in ATPase activity, a decrease in the viscosity of the salt solution, agglomeration of protein molecules, and spatial structure changes such as

n9 After protein denaturation, the water holding capacity of muscle tissue decreases, the texture becomes harder, and the mouthfeel deteriorates. When used as a food processing material, the processing suitability decreases.

If frozen and denatured fish meat with protein is used as the raw material for processed surimi products, the product will lack flexibility.

Food organization changes in supermarket refrigerated showcase. Because plant tissues suffer more damage than animal tissues during freezing, vegetable and fruit plant foods generally undergo

blanching or sugaring before freezing. The structure of plant cells is different from animal cells. There are large vacuoles in plant cells, which keep the plant tissues at a high water content

, but the high water content during freezing causes great damage to the cells. There is a cell wall dominated by cellulose outside the cell membrane of plant cells, while animal cells only have cell membranes,

. The cell wall is thicker and less elastic than the cell membrane. It is easy to rupture when frozen and damage the cell. In addition, the composition of plant cells and animal cells are different, especially

. The content of high molecular protein and carbohydrates is different, and the composition of organic matter is also different. Due to these differences, under the same freezing conditions, the amount of ice crystals

, position, size, and shape are different, resulting in different degrees of mechanical damage and colloidal damage. Fresh fruits, vegetables and other plant foods are vital

organisms, and their plant cells will be killed during the freezing process. This is related to the fact that the water in the cells becomes ice crystals when the plant tissues freeze. After the plant freezes to death, it will brown the fruits and vegetables due to the increased activity of oxidase enzymes

. In order to maintain the original color and prevent browning, vegetables are generally blanched before quick-freezing, while animal food

products do not require this process because they are inactive cells.

Biological and microbial changes. Creatures here refer to small creatures, such as insects and parasites, which will die after freezing. The cysts without

that are parasitic in beef and pork will die when frozen. The larvae of Trichinella in pork died after 20 days at -15°C.

of the split head tapeworm in salmonThe larvae of

died at -15°C for 5 days. Since freezing can kill the parasites in meat, some countries make regulations on the freezing state of meat. The Food and Agriculture Organization of the United Nations

Organization (FAO) and the World Health Organization (WHO) jointly recommend that when meat parasite pollution is not serious, it should be stored at -10°C for at least 10 days. Microorganisms that cause food spoilage

include bacteria, molds and yeasts. Among them, bacteria are most related to food spoilage and food poisoning. The growth and reproduction of microorganisms require certain environmental conditions. Temperature is one of the important conditions. When the temperature is lower than the optimum temperature, the growth of microorganisms is inhibited: when the temperature is lower than the minimum temperature, micro

organisms cease to multiply. The bacteria that cause food poisoning are generally mesophilic bacteria, which slow down below 10°C and stop propagation below 4.5°C. Mold and spoilage of fish

Bacteria are generally low temperature bacteria, which multiply slowly below 0℃ and stop multiplying below -lo℃. Freezing prevents the growth and reproduction of microorganisms. Food is stored in a frozen state

, the number of contaminated microorganisms before freezing will gradually decrease with time, but it is not expected that freezing can kill the contaminated microorganisms, as long as the temperature rises, the microbial

> >> >> n9 Therefore, it is necessary to reduce bacterial contamination as much as possible before the food is frozen to ensure the quality of the frozen product. Freezing prevents the growth and reproduction of bacteria,

But because the enzymes produced by the bacteria are still active, although the activity is small, it still has an effect. It slows the biochemical process and reduces the quality of the food. Therefore, freeze the food

> >

n9 There is still a certain period. When food is at -10°C, most of the water has frozen into ice, the concentration of the remaining solution increases, the water activity decreases, and bacteria cannot multiply.

So -10℃ is the highest temperature limit for frozen food. The International Refrigeration Association (IIR) recommends that in order to prevent microorganisms from multiplying, frozen food must be stored below -12℃

. In order to prevent the effect of enzymes and physical changes, the temperature of frozen food in supermarket refrigerated showcase must be lower than -18℃.

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Food supermarket refrigerated showcase principle of preservation (four)

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